1. Field of the Invention
The present invention relates to optical communication devices used in optical communications and to laminated optical communication modules constituting optical communication devices.
2. Description of the Related Art
The spread of the Internet in recent years has burgeoned a need for the high speed transmission and reception of large quantities of information, such as music, moving images, and computer data. Using optic fibers, data can be sent and received at transfer speeds of 100 Mbps or more for private households. This use of optical fibers allows data to be sent and received at speeds approximately three magnitudes of power faster than with modems or ISDN, which use telephone lines and are widely used in general households. Moreover, in trunk systems, the transmission speed reaches 10 to 40 Gbps. The recent introduction of the new technology called “optical multiplexing transmission” has allowed even faster transfer speeds and larger data amounts.
It is expected that these advances in optical communications will be accompanied by a demand in the field of optical communication devices for progress in technologies for optically coupling optical waveguides such as optic fibers, and elements such as light-receiving elements and light-emitting elements.
Conventionally, an optic fiber and a light-emitting element were optically coupled in a configuration in which light from the light-emitting element was focused by a lens and coupled into the optic fiber (JP S61-93419A).
On the other hand, there are also methods in which an optical waveguide and a light-emitting element or a light-receiving element are coupled without using an optical system such as a lens. With a method for directly coupling a semiconductor laser and an optic fiber, the end of the optic fiber is cut away and its outer ferrule is notched into a L-shape so that chip bonding can be performed. That portion of the outer ferrule notched into an L-shape is adhered to the semiconductor laser, and the center of the optic fiber core and the center of the point of emission of the semiconductor laser chip are aligned (JP S63-253315A). In another method for directly coupling a semiconductor laser chip and an optical waveguide, a gap is provided between the end surface of the active layer of a semiconductor laser and the end surface of the optical waveguide. The semiconductor laser and the optical wavegide are arranged in opposition to one another so that the light is coupled directly into the optical waveguide (JP H3-39913A).
With these conventional light coupling methods, there was the problem that it was difficult to efficiently make light from the light-emitting element incident on the optical waveguide because either an optical distance existed between the light-emitting surface of the light-emitting element and the optical waveguide or various types of optical systems were provided between the light-emitting element and the optical waveguide, thus making it difficult for the devices to be made compact.
With these problems in mind, many light-coupling configurations that achieve light processing functions and also allow the devices to be made compact have been proposed. For example, there has been disclosed a light-coupling component constituted by a five-layered waveguide structure in which a plurality of substrates are arranged three-dimensionally to serve as a means for achieving a compact integrated optical circuit (JP S61-148406A). However, although JP S61-148406A presents an example of a three-dimensional optical circuit component, it adopts a method for connecting the vertical light path and the horizontal light path that exploits the difference in refractive indices between the outside air and the substrates. Thus, the transfer of light power between the vertical light path and the horizontal light path requires a so-called “complete coupling length.” Consequently, it was not possible to sharply bend the light path. Moreover, because of this, if the three-dimensional optical circuit was made by stacking a plurality of horizontal circuit boards on top of one another, then it was necessary to provide a predetermined spacing between the horizontal circuit boards. Thus, the horizontal circuit boards could not be adhered to one another.
On the other hand, JP S54-139847A discloses an example in which a reflective layer is provided on the inner surface of the optical waveguide. However, the reflective layer is formed by processing the inner surface of a bendable tube for a laser processing machine. In other words, the publication does not indicate the sharp bending of the light path, nor does it disclose a three-dimensional optical circuit. Also, FIG. 1 of this publication shows that the light path of this conventional laser processing machine is constituted by open space and a reflective mirror, however, the light path is not formed within a substrate.
Also, JP H2-73311A discloses the formation of a hollow waveguide made of gold. However, the gold optical pipe remaining as the outer casing is not bent sharply but rather is formed in a spiral shape. When the optical pipe is bent sharply it is difficult to secure the light path within the pipe.
JP H10-170765A discloses the formation of a V-groove in the surface of a silicon substrate through anisotrophic etching, forming a reflective film on the oblique walls of the V-groove, and then burying an optic fiber inside the V-groove. The light-emitting element or the light-receiving element and the optic fiber are coupled to one another via the reflective film. However, with this method the optic fiber must be arranged in a straight line, and it is not possible to form a waveguide that is bent freely in the horizontal surface.
JP 2001-133645A discloses metalizing the upper surface, lower surface, and side surfaces of a substrate in which a waveguide is formed in order to block out aberrant light from the waveguide substrate. However, there is no disclosure of metalizing the waveguide itself and bending the light path sharply.
JP H2-9183A mentions an apparatus that serves as an optoelectronic device assembly in which a groove portion is provided in a substrate and a reflector is partially provided on an end face of the groove portion. In this apparatus, an optic fiber is inserted into the groove portion and a device is arranged above the reflector, so that the optic fiber and the device are coupled through the reflector. However, in this apparatus, light is transmitted to the device via the optic fiber, and thus there are limits as to how compact the apparatus can be made.
JP H5-264833A mentions a waveguide made by forming a resist layer, which is an applied layer, on a substrate, forming a cavity within the resist, and then forming a reflective film on the inside wall of the cavity. However, the waveguide is not formed within the substrate but rather is formed inside the resist layer formed on the substrate. The shape of the resist is easily altered due to the outside environment (for example, temperature) or stress, and thus it is difficult to secure sufficient durability with a waveguide that is formed inside a resist layer.